Idk, that sounds quite strange. Just thinking about it, that means it would be on 7nm and all the power savings of going that route will be negated by doing it with gddr6. So essentially you'll have a V64, just with different memory type, and perhaps not even as fast since if we look at 2070 vs V64 it's 448 GB/s vs 484 GB/s and we know for sure it's going to take a lot more bandwidth until there's a point of diminishing returns based on the VII. And would it even be cheaper to do it with GDDR6? R&D notwithstanding for actually getting Vega to work with GDDR6, the memory itself doesn't seem to be cheaper than HBM2 at this point.
We might be overthinking this, and the Vega logos are just for the APU branding.